What new weapons or improvements on old weapons made the Civil War the deadliest war in U. S, history?

Machine guns and repeating rifles

Explanation:

Machine guns were used in the Civil War. Compared to the powder muskets of the revolutionary war, These guns didn't need to be reloaded as often and as a result could inflict more casualties on the opposing side. They were also an all around improvement, with better accuracy then their primitive counterparts.

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frederick william of brandenburg-prussia trained his son, frederick, to be a hardy soldier. but frederick disliked rifle shooting and horseback riding. unlike his father, he was interested in french literature. he enjoyed poetry and music and, like some others of the enlightenment, he scoffed at religion. his father thought him soft, frivolous and unmindful of his duties. and when frederick refused to put his signature on a right to succession, for a few moments his father strangled him.